The VDP sensor is usually made of piezoresistive material such as silicon, and its resistance can be measured from knowing the current ([I.sub.AB]) and voltage ([V.sub.CD]).
The original theory was developed first by van der Pauw [5, 6] to calculate the "change in resistance" for a given piezoresistive material. For a planar isotropic piezo-resistive conductor of arbitrary shape with no discontinuity, VDP theorem defines the "resistance" -[R.sub.AB,CD] as the potential difference ([V.sub.D] - [V.sub.C]) between contacts D and C per unit current through contacts A and B, [I.sub.AB] (see (1)).
For example, polypyrrole is a piezoresistive material
combined with rubbers to create elastic, electrically conductive yarns .
Polysilicon is chosen as the piezoresistive material
which senses the movement of the membrane.
Four copper contact pads are used on the piezoresistive material
, two for supply voltage input and two for sensor outputs as shown in Figures 4 and 5.
Silicon exhibits a high gauge factor and is principally applicable as a piezoresistive material
up to temperatures of 400[degrees]C .
The instrument is made of a piezoresistive material
that changes voltage as its capacitance is altered by gas velocity.
Due to imperfections in manufacturing and non-ideal contact between the piezoresistive material
and the electrodes, there are different responses from neighbouring cells for the same stimuli (up to 5% of the whole range).
Through various design configurations, piezoresistive materials
can be used for force, pressure, and flexure sensing [1, 3].
Chen, "Piezoresistive materials
from directed shear-induced assembly of graphite nanosheets in polyethylene," Advanced Functional Materials, vol.
Key words: tactile sensors, piezoresistive materials
, robotics, PVDF, piezoelectricity, object recognition